This invention relates in general to vehicular brake systems and in particular is concerned with Bernoulli force during the operation of isolation valves in hydraulic braking systems.
Hydraulic braking systems for vehicles are well known. A typical hydraulic brake system includes a master cylinder connected via fluid conduits to wheel brakes. The master cylinder generates hydraulic forces by pressurizing brake fluid when the driver steps on the brake pedal. During a normal braking event, the pressurized fluid travels through the fluid conduits to actuate brake cylinders in the wheel brakes and slow the vehicle.
Anti-lock braking systems (ABS) are a feature of most modern hydraulic braking systems. A hydraulic control unit (HCU) or housing, containing control valves and other components such as low pressure accumulators and pumps, is located between the master cylinder and the wheel brake assemblies. An electronic controller connected to a variety of sensors operates the HCU to selectively control pressure to the wheel brake assemblies to provide an appropriate braking response.
Low pressure accumulators are provided in the HCU between a control valve known as a dump valve and an inlet to a pump. During an anti-lock (ABS) event, pressurized fluid is dumped from a wheel brake by opening a dump valve so that such fluid can travel to a low pressure accumulator. Fluid in the low pressure accumulator is pumped to an inlet of a control valve known as an isolation valve for reapply events of the brake system.
During braking events, isolation valves close and open and Bernoulli forces in the fluid resist the opening of the isolation valves. During a normal braking event when the valve is fully open, these Bernoulli forces are undesirable because they tend to close isolation valves thereby influencing the responsiveness of the breaking system and the distance required for completely stopping the vehicle. In contrast, during an ABS or other controlled braking event, these Bernoulli forces are desirable because they reduce the magnetic force required to hold the valve in a partially open condition.
Thus, it is desirable to reduce Bernoulli forces during normal braking events to increase isolation valve operation speed and improve response time and stopping distance without disrupting Bernoulli forces generated during controlled braking events.
This invention involves an improved armature for use in isolation valves in hydraulic braking systems. The improved armature is shaped to reduce Bernoulli forces during normal braking events to improve response time and stopping distance without disrupting Bernoulli forces generated during controlled braking events.
The isolation valve for controlling fluid flow in a vehicular braking system according to the present invention comprises a solenoid coil assembly and an armature moveably positioned within the solenoid coil assembly. In one embodiment, the armature has a ball end engaging a ball seat and an edge groove at the ball end to modify Bernoulli force that affects movement of the armature when the solenoid coil assembly is de-energized.
Another embodiment of the invention is an isolation valve for use in a hydraulic control unit for a vehicular brake system where the isolation valve comprises a valve body housing defining a valve cavity and a valve stem mounted in the valve cavity. The valve stem has a coaxial fluid passage therethrough. A cylindrical sleeve is mounted on the valve body surrounding the valve stem and an armature is slidably mounted in the cylindrical sleeve and biased by a spring in a normally open position. The armature has a valve end for controlling fluid flow through the coaxial fluid passage, and an outer step at the valve end to modify Bernoulli force that affects movement of the armature.
Another embodiment of the invention is an isolation valve for use in a hydraulic control unit for a vehicular brake system where the isolation valve comprises a valve body housing defining a valve cavity and a valve stem mounted in the valve cavity. The valve stem has a coaxial fluid passage therethrough. A cylindrical sleeve is mounted on the valve body surrounding the valve stem and an armature is slideably mounted in the cylindrical sleeve and biased by a spring in a normally open position. The armature has a valve end for controlling fluid flow through the coaxial fluid passage, and an annular cavity at the valve end to modify Bernoulli force that affects movement of the armature.
Still another embodiment of the invention is an isolation valve for use in a hydraulic control unit for a vehicular brake system where the isolation valve comprises a valve body housing defining a valve cavity and a valve stem mounted in the valve cavity. The valve stem has a coaxial fluid passage therethrough. A cylindrical sleeve is mounted on the valve body surrounding the valve stem and an armature is slideably mounted in the cylindrical sleeve and biased by a spring in a normally open position. The armature has a valve end for controlling fluid flow through the coaxial fluid passage, and an annular cavity and an outer step at the valve end to modify Bernoulli force that affects movement of the armature.
A further embodiment of the invention is a method of manufacturing an isolation valve for use in a hydraulic control unit for a vehicular brake system comprising the steps of: forming a valve cavity in a valve body housing; mounting a valve stem mounted in the valve cavity, the valve stem having a coaxial fluid passage therethrough; mounting a cylindrical sleeve in the valve body surrounding the valve stem; forming an armature having a valve end for controlling fluid flow through the coaxial fluid passage; configuring the valve end to modify Bernoulli force that affects movement of the armature; mounting the configured armature in the cylindrical sleeve so that it is slideable and biased by a spring in a normally open position. The valve end may be configured to modify Bernoulli force with an edge groove, an outer step, an annular cavity, or a combination of an outer step and an annular cavity.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.